Guide
MIM or Die Casting for Small Metal Parts: When Does Steel Beat Zinc and Aluminum?
MIM or die casting is a choice between two molding-style metal processes that share shape freedom but not alloys: die casting forms aluminum, magnesium, zinc and ZA, while metal injection molding forms steels, stainless steels and other alloys. The decision is rarely about which process is better; it is about whether the part needs steel properties in a small, complex shape.
By Saola Manufacturing engineering team · Published · Updated
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Do MIM and die casting actually compete on the same part?
Rarely on the same alloy. NADCA lists four die casting alloy families, aluminum, magnesium, zinc and ZA, none of them steel, while MIM is a steel and stainless process at heart, so the real question is whether the part needs steel properties.
The die casting side is stated plainly by the trade association: the four families of die casting alloys offer wide latitude for trade-offs in design and economic factors (NADCA, Alloy Selection). On the MIM side, MIMA lists iron, low-alloy steels, several stainless families, tool steels, nickel-base and copper alloys among its materials, and says stainless steels account for nearly half of commercial MIM activity (MIMA, MIM Materials Range). The two lists barely overlap.
So the comparison almost never starts with a clean-sheet choice. It starts with a small zinc or aluminum die-cast part that is failing in service on strength, wear or corrosion, or with a buyer who has been quoted both and wants to know why the numbers differ so much. This guide covers when moving to MIM is the right response, what changes on the drawing, and how to compare the two quotes.
How similar is the shape freedom of the two processes?
Very similar. MPIF states that the MIM process is very similar to plastic injection molding and high-pressure die casting, and MIMA says MIM offers the same design freedom as plastic injection molding.
Both statements are in the trade literature (MPIF, Metal Injection Molding and MIMA, Designing with MIM). MIMA lists cross holes, internal threads, undercuts and cantilevers as geometries well suited to MIM. A die cast part can carry ribs, bosses, thin walls and integrated features in the same way, and for that reason a part drawn for die casting often translates to MIM without a redesign of its overall form.
The differences are in detail rules. Both use a parting plane, draft and fillets, and both put the gate at a considered location. MIM adds a rule that die casting does not have: the molded part is about 20% larger than the finished part and shrinks during sintering, so large flat areas and long unsupported sections need thought for distortion (MIMA, Complex Designs with MIM). The die casting side is covered in the guides on draft angle and minimum wall thickness.
When does the part need steel properties?
When strength, wear or corrosion resistance in service exceeds what a zinc, aluminum or magnesium alloy provides at the section sizes you can afford. That is the one trigger that reliably justifies moving a die-cast shape to MIM.
The table sets out the material differences from the two associations’ own pages. The practical reading is that die casting gives you a family of lightweight, low-melting alloys with excellent shape freedom, and MIM gives you the same kind of shape in a steel. A zinc latch that wears, a zinc gear that strips, an aluminum lever that yields, or a die-cast nozzle that corrodes in a wet environment are the typical triggers.
Two cautions. First, a stainless MIM part is not automatically stronger than every die cast part in every dimension; it is stronger where you need steel’s properties, and MIMA says near-full density and heat treatability are what make that possible (MIMA, Designing with MIM). Check the property you actually need, such as yield, hardness or fatigue life, against the grade’s published values in the standard (ASTM B883, ISO 22068 or MPIF Standard 35-MIM), which are sold, not free. Second, if the problem is corrosion rather than strength, NADCA notes that the major differences in corrosion resistance occur within the alloy groups and that low-cost surface treatments can improve any of them, so a better die casting alloy or a finish may solve it without a new process.
| Topic | Die casting (zinc, aluminum, magnesium, ZA) | Metal injection molding |
|---|---|---|
| Alloy families | Aluminum, magnesium, zinc and ZA (four families) | Iron and low-alloy steels, austenitic, duplex, ferritic, martensitic and precipitation-hardening stainless, tool steels, nickel, copper and others |
| Strength | ZA alloys have the highest ultimate and yield strengths of the four die cast families | Mechanical properties nearly equivalent to wrought materials (MPIF) |
| Density | Not stated in the NADCA page used here | 96% to 99% of theoretical density after sintering |
| Very small parts | Zinc and ZA-8 are the usual choice for castings typically under one ounce (28 g) | Small complex parts; MIMA gives no weight limit |
| Corrosion | Largest differences are within each alloy group; low-cost surface treatments can improve any alloy | 316L and 17-4PH are the most popular alloys; interconnected porosity typically under 0.2%, so plating and coloring need no special preparation |
| Heat treatment | Not covered on the NADCA page used here | Same methods as wrought counterparts, such as quenching and tempering |
| Material callout | The die casting alloy designation | A MIM grade and condition under ASTM B883 or ISO 22068; ISO 22068 covers MIM only |
How do the cost structures compare?
Both processes need a hardened steel tool and both reward volume, so the useful comparison is the loaded cost of the finished part, not the piece price of the molded or cast blank.
MIMA states that MIM suits medium to high volumes, thousands to millions of parts a year, to offset tooling and start-up engineering (MIMA, Designing with MIM). NADCA does not publish a comparable volume statement on its alloy selection page, and published comparisons from suppliers differ from one another, so treat any single “MIM costs more than die casting by this factor” claim as unverified. The sound approach is to get both quotes on the same drawing with tooling on its own line.
Look at what each quote leaves out. A die cast part commonly needs machining on sealing faces and threads, and the porosity that machining exposes is the subject of the guide on die casting porosity after machining. A MIM part may need a secondary operation such as coining, machining or heat treatment, and MIMA notes these add to component cost (MIMA, Secondary Operations with MIM). A stainless MIM part may avoid a plating or coating line entirely, which is a cost the die cast quote carries.
What changes on the drawing when you move from die casting to MIM?
The alloy callout, the tolerance basis and the finishing notes change; the shape mostly does not. MIM tolerances are expressed as a percentage of size and the material is called out to a MIM standard, not a die casting one.
Replace the die casting alloy designation with a MIM grade and its standard, for example a 316L or 17-4 PH grade under ASTM B883 or ISO 22068. ISO 22068 covers MIM materials only and says it does not apply to structural parts made by press-and-sinter or powder forging, so it should not be cited for a pressed part (ISO 22068:2012). ASTM B883 covers ferrous MIM materials and ASTM lists B883-19 as historical, with B883-24 current, so cite the edition you mean (ASTM B883 store page).
Next, rethink the tolerances. MIMA gives the average MIM tolerance as within plus or minus 0.3% of the dimension (MIMA, Secondary Operations with MIM), so a feature that die casting held with a fixed tolerance may need to be sized or machined after sintering. Mark those features on the drawing. Finally, drop finishing notes that existed only because the die casting alloy needed protection, and keep the ones that serve a function.
How should you compare a MIM quote with a die casting quote?
Put both on the same drawing, volume and acceptance criteria, then compare the loaded part cost including secondary operations, finishing and tooling. If either quote leaves out an operation the drawing needs, it is not yet comparable.
Ask each supplier to state the material and its standard, the number of cavities, which features are held as formed and which are machined, the finishing included, and who owns the tool. For the die casting quote, ask what happens to porosity at machined faces. For the MIM quote, ask for the sintered density and the treatment of the sealing and thread features.
Saola places die casting and MIM through partner plants it manages and does not name them, and runs CNC turning and milling at its lead partner plant, so a mixed-process part can be quoted with each step stated and the production site and country of origin named on the quote. See the MIM and powder metal page and the die casting page for what is placed where.
Frequently asked
Is MIM stronger than die casting?
Where the part needs steel, yes: MIM can reach mechanical properties nearly equivalent to wrought materials according to MPIF, while the strongest die casting family listed by NADCA is ZA. For parts that are adequate in zinc or aluminum, the stronger material is not needed and die casting may be the simpler route.
Can a die cast zinc part be redesigned for MIM stainless?
Usually yes, because the shape freedom is similar. Expect changes to the wall and rib rules, to the tolerance basis and to how the part is supported during sintering, and plan to prototype by machining first.
Does MIM replace die casting for larger parts?
Not generally. NADCA points to aluminum for medium-to-large structural parts, and MIM is a small-part process. MIMA does not state a weight limit, so ask the supplier for the largest part they mold in the grade you need.
Which process has less porosity?
MIMA reports 96% to 99% of theoretical density after sintering (MIMA, Process Overview), and PickPM describes MIM among near-fully dense processes with residual porosity often under 1% (PickPM, Consolidation Processes). Die casting porosity depends on the alloy, the process and the part; see the guide on porosity after machining.
Do I still need plating on a stainless MIM part?
Often not for corrosion, since the stainless grade provides it. MIMA says interconnected porosity is typically under 0.2%, so plating and coloring do not need special preparation when you do want them for appearance.
Sources
- NADCA, Alloy Selection, North American Die Casting Association design pages, accessed October 2026
- MIMA, MIM Materials Range, Metal Injection Molding Association, accessed October 2026 (page copyright 2026)
- MIMA, Designing with MIM, Metal Injection Molding Association, accessed October 2026 (page copyright 2026)
- MIMA, Secondary Operations with MIM, Metal Injection Molding Association, accessed October 2026 (page copyright 2026)
- MPIF, Metal Injection Molding (Intro to PM), Metal Powder Industries Federation, accessed October 2026
- PickPM, Consolidation Processes, MPIF powder metallurgy design center, accessed October 2026
- ISO 22068:2012, sintered metal injection-molded materials, specifications, ISO, published June 2012 (Standards Council of Canada listing, accessed October 2026)
- ASTM B883, Standard Specification for Metal Injection Molded (MIM) Materials, ASTM International store page, B883-19 listed as historical, B883-24 as current (page updated 2024)